Network Working Group H. Tschofenig
Internet-Draft ARM Limited
Intended status: Informational S. Farrell
Expires: August 7, 2017 Trinity College Dublin
February 3, 2017
Report from the Internet of Things (IoT) Software Update (IoTSU)Workshop 2016draft-iab-iotsu-workshop-01.txt
Abstract
This document provides a summary of the 'Workshop on Internet of
Things (IoT) Software Update (IOTSU)' which took place at Trinity
College Dublin, Ireland on the 13th and 14th of June, 2016. The main
goal of the workshop was to foster a discussion on requirements,
challenges and solutions for bringing software and firmware updates
to IoT devices. This report summarizes the discussions and lists
recommendations to the standards community.
Status of This Memo
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This Internet-Draft will expire on August 7, 2017.
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are partly out of the scope for the Internet Engineering Task Force
(IETF). This long-term planning function of the IAB is complementary
to the ongoing engineering efforts performed by working groups of the
IETF.
In his essay 'The Internet of Things Is Wildly Insecure And Often
Unpatchable' [BS14] Bruce Schneier expressed concerns about the
status of software/firmware updates for Internet of Things (IoT)
devices. IoT devices, which have a reputation for being insecure
already at the time when they are manufactured, are often expected to
stay active in the field for 10+ years and operate unattended with
Internet connectivity.
Incorporating a software update mechanism to fix vulnerabilities, to
update configuration settings as well as adding new functionality is
recommended by security experts but there are challenges when using
software updates, as the United States Federal Trade Commission (FTC)
staff in their "Internet of Things - Privacy & Security in a
Connected World" [FTC] and the Article 29 Working Party Opinion
8/2014 on the on Recent Developments on the Internet of Things [WP29]
reported.
Amongst the challenges in designing a basic software/firmware update
function are:
- Implementations of software update mechanisms may incorporate
vulnerabilities becoming an attractive attack target, see for
example [OS14],
- Operational challenges such as the case of an expired certificate
in a hub device [BB14],
- Privacy issues if devices "call home" often to check for updates
- A lack of incentives to distribute software updates along the
value chain
- Who should be able to update device software after normal support
stops? When should an alternate source of software updates take
over?
There are various (often proprietary) software update mechanisms in
use today and the functionality of those varies significantly with
the envisioned use of the IoT devices. More powerful IoT devices,
such as those running general purpose operating systems (like Linux),
can make use of sophisticated software update mechanisms known from
the desktop and the mobile world. This workshop focused on more
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constrained IoT devices that often run dedicated real-time operating
systems or potentially no operating system at all.
There is a real risk that many IoT devices will continue to be
shipped without a solid software/firmware update mechanism in place.
Ideally, IoT software developers and product designers should be able
to integrate standardized mechanisms that have experienced
substantial review and where the documentation is available to the
public.
Hence, the IAB decided to organize a workshop to reach out to
relevant stakeholders to explore the state-of-the-art and to identify
requirements and gaps. In particular, the call for position papers
asked for
- Protocol mechanisms for distributing software updates.
- Mechanisms for securing software updates.
- Meta-data about software / firmware packages.
- Implications of operating system and hardware design on the
software update mechanisms.
- Installation of software updates (in context of software and
hardware security of IoT devices).
- Privacy implications of software update mechanisms.
- Implications of device ownership and control for software update.
The rest of the document is organized as follows: Basic terminology
is provided in Section 2 followed by a longer section discussing
requirements. Subsequent sections explore selected topics, such as
incentives, and measurements, in more detail. Most of the writeup
does raise more questions than it answers. Nevertheless, we tried to
synthesise possible conclusions and offer a few next steps.
2. Terminology
As is typical with people from different backgrounds, workshop
participants started the workshop with a discussions of terminology.
This section is more intended to reflect those discussions than to
present canonical definitions of terms.
Device Classes: IoT devices come in various "sizes" (such as size of
RAM, or size of flash memory). With these configurations devices
are limited in what they can support in terms of operating system
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features, cryptographic algorithms, and protocol stacks. For this
reason, the group differentiated two types of classes, namely ARM
Cortex A-class / Intel Atom and Cortex M-class / Intel Quark types
of devices. A-class devices are equipped with powerful processors
typically found in set-top boxes and home routers. The Raspberry
Pi is an example of a A-class device, which is capable of running
a regular desktop operating system, such as Linux. There are
differences between the Intel and the ARM-based CPUs in terms of
architecture, micro-code and who is allowed to update a BIOS (if
available) and the micro-code. A detailed discussion of these
hardware architectural differences were, however, outside the
scope of the workshop. The implication is that lower-end
microcontrollers have constraints that put restrictions on the
amount of software that can be put on them. While it is easy
require support of a wide range of features those may not
necessarily fit on these devices.
Software Update and Firmware Update: Based on the device classes it
was observed that regular operating systems come with
sophisticated software update mechanisms (such as RPM [rpm] or
Pacman [pacman]) that make use of the operating system to install
and run each application in a compartmentalized fashion. Firmware
updates typically do not provide such a fine-grained granularity
for software updates and instead distribute the entire binary
image, which consists of the (often minimalistic) operating system
and all applications. While the distinction between the
mechanisms A-class and M-class devices will typically use may get
more fuzzy over time, most M-class devices use firmware updates
and A-class devices use a combination of firmware and software
updates (with firmware updates being less frequent operations).
Hitless Update: A hitless update implies that the user experience is
not "hit", i.e., it is not impacted. It is possible to impact the
user experience when applying an update even when the device does
not reboot (to obtain or apply said update). If the update is
applied when a user is not using a product and their service is
not impacted, the update is "hitless".
3. Requirements and Questions Arising
Workshop participants discussed requirements and several of these
raised further questions. As with the previous section we aim to
present the discussion as it was.
- There may be a need to be support partial (differential) updates,
that do not require the entire firmware image to be sent. This
may mean that techniques like bsdiff [bsdiff] and courgette
[courgette] are used but might also mean devices supporting
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download of applications and libraries alone. The latter feature
may require dynamic linking and position independent code. It was
unclear whether position independent code should be recommended
for low-end IoT devices.
- The relative importance of dynamic linkers for low-end IoT devices
is unclear. Some operating systems used with M-class devices,
such as Contiki, provide support for a dynamic linker according to
[OS-Support]. This could help to minimize the amount of data
transmitted during updates since only the modified application or
library needs to be transmitted.
- How should dependencies among various software updates be handled?
These dependencies may include information about the hardware
platform and configuration as well as other software components
running on a system. For firmware updates the problem of
dependencies are often solved by the manufacturer or OEM rather
than on the device itself.
- Support for devices with multiple micro-controllers may required
an architecture where one micro-controller is responsible for
interacting with the update service and then dispatching software
images to the attached micro-controllers within its local realm.
The alternative of letting each microcontroller interact with an
update service appeared less practical.
- Support may be required for devices with multiple owners/
stakeholders where the question arises about who is authorized to
push a firmware/software update.
- Data origin authentication (DAO) was agreed to be required for
software updates. Without DAO, updates simply become a perfect
vulnerability. It is however non-trivial to ensure the actual
trust relationships that exist are modelled by the DAO mechanism.
For some devices and deployment scenarios, any DAO mechanism is
onerous, possibly to the point where it may be hard to convince a
device-maker to include the functionality.
- Should digital signatures and encryption for software updates be
recommended as a best current practice? This question
particualrly raises the question about the use of symmetric key
cryptography since not all low end IoT devices are currently using
asymmetric crypto.
- DAO is most commonly provided via digital signature mechanisms,
but symmetric schemes could also be developed, though IETF
discussion of such mechanisms (for purposes less sensitive than
software update) has proved significantly controversial. The main
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problem seems to be that simple symmetric schemes only ensure that
the sender is a member of a group and do not fully authenticate a
specific sender. And with software update, we do not want any
(possibly compromised) device to be able to be authenticate new
software for all other similar devices.
- What are the firmware update signing key requirements? Since
devices have a rather long lifetime there has to be a way to
change the signing key during the lifetime of the device.
- Should a firmware update mechanism support multiple signatures of
firmware images? Multiple signatures can come in two different
flavours, namely
a single firmware image may be signed by multiple different
parties. In this case one could imagine an environment where
an Original Equipment Manufacturer (OEM) signs the software it
creates but then the software is again signed by the enterprise
that approves the distribution within the company. Other
examples include regulatory signatures where a the software for
a medical device may be signed as approved by a certification
body.
a software image may contain libraries that are each signed by
their developers.
Is a device expected to verify the different types of signatures
or is this rather a service provided by some non-constrained
device? This raises the question about who the IoT device should
trust for what and whether transitive trust is acceptable for some
types of devices?
- Are applications from a range of sources allowed to run on a
device or only those from the OEM? If the device is a "closed"
device that only supports/runs software from the OEM then a single
signature may be sufficient. In any more "open" system, 3rd party
applications may require support of multiple signatures.
- There is a need for some form of secure storage, at least for
those IoT devices that are exposed to physical attacks. This
includes at least the need to protect the integrity of the public
key of the update service on the device (if signature based DAO is
in use). The use of symmetric key cryptography requires improved
confidentiality protection (in addition to integrity protection).
- Is there a need to allow the update infrastructure-side to
authenticate the IoT device before distributing an update?
Questions about the identifier used for such an authentication
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action were raised. The idea of re-use MAC addresses lead to
concerns about the significant privacy implications of such
identifier re-use.
- It is important to minimize device/service downtime due to update
processing, minimize user interaction (e.g., car should not
distract the driver) (see hitless updates). While it may not be
possible to avoid all downtime, there was agreement that one ought
strive for "no inappropriate" device downtime. This means minimal
downtime impacting the user/operation of the device. The
definition of "downtime" also depends on the use case, with a
smart light bulb, the device could be "up" if the light is still
on, even if some advanced services are unavailable for a short
time. Whether an update can be done without rebooting the device
depends on the software being installed, on the OS architecture,
and potentially even on the hardware architecture. The cost/
benefit ratio also plays a role.
- It is desirable to minimise the time taken from the start of the
update to when it is finished. In some systems with many devices
(e.g., industrial lighting) this can be a challenge if updates
need to be unicasted.
- In some systems with multiple devices, it can be a challenge to
ensure that all devices are at the same release level, especially
if some devices are sleepy. There are some systems where ensuring
all relevant devices are at the same release level is a hard-
requirement. In other cases, it is acceptable if devices converge
much more slowly to the current release level.
- It ought not be possible for a factory worker to compromise the
update process (e.g., copy signing keys, install unauthorized
public keys/trust anchors) during the manufacturing process.
There are typically two factories involved, first the factory that
produces microcontrollers and other components. The second
factory produces the complete product, such as a fridge. This
fridge contains many of the components previously manufactured.
Hence, the firmware of components produced in the first stage may
be 6 month old when the fridge leaves the factory. One does not
want to install a firmware update when the fridge boots the first
time. For that time the firmware update happens already at the
end of the manufacturing process.
- Should devices have a recovery procedure when the device gets
compromised? How is the compromise detected?
- There was a bit of discussion about the importance for IoT devices
to know the current time for the purpose of checking certificate
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validity. For example, what does "real-time clock" (RTC) actually
mean? And what constitute 'good enough' time? There are,
however, cost, power, size, and environmental constraints that can
make the addition of a real-time clock to an IoT device complex:
o Cost: battery- or supercap-backed RTC modules might be several
times the cost of the rest of the bill of materials.
o Size: the battery and other components are often several times
larger than the rest of the material.
o Manufacturing: some modules require an extra assembly step,
because the battery could be damaged/explodes at high
temperature during the reflow process.
o Supply chain: devices containing fitted batteries need
additional supply chain management to account for storage
temperature and to avoid shipping aged devices.
o Environmental: Real-time-clock modules are typically not rated
at industrial temperature ranges. Those that are have
extremely reduced lifetime at high temperatures.
o Lifetime: some of these modules last only a few years at the
top of their environmental range.
While a good solution is needed, it is not clear whether there is
one true solution. A recent proposal from Google called Roughtime
[RT] may be worthwhile to explore.
- How do devices learn about a firmware update? Push or Pull? What
should be required functionality for a firmware update protocol?
- There is a need to find out whether a software update was
successful. In one discussed solution the bootloader analyses the
performance of the running image to determine which image to run
(rather than just verifying the integrity of the received image).
One of the key criteria is that the updated system is able to make
a connection to the device management/software update
infrastructure. As long as it is able to talk to the update
infrastructure it can receive another update. As alternative
perspective the argument was made that one needs to have a way to
update the system without have the full system running.
- Gateway requirements. In some deployments gateways terminate the
IP-based protocol communication and use non-IP mechanisms to
communicate with other micro-controllers, for example, within a
car. The gateway in such a system is the end point of the IP
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communication. The group had mixed feelings about the use of
gateways vs the use of IP communication to every micro-controller.
Participants argued that there is a lack of awareness of IPv6
header compression (with the 6lowpan standards) and of the
possible benefits of IPv6 in those environments in terms of
lowering the complexity of the overall system.
- The amount of energy consumed due to software update needs to be
minimized. For example, awakening a sleepy device regularly only
to check for new software would seem wasteful if the device cannot
feasibly be exploited whilst asleep. However, the trade-off is
that once the device awakens with old software, there may be a
window of vulnerability, if some relevant exploit has been
discovered.
- The amount of storage required for update ought be minimized and
can sometimes be significant. However, there are also benefits to
schemes that store two or three different software images for
robustness, e.g., if one has space for separate current, last-
known-good and being-updated images then devices can better
survive the buggy occasional updates that are also inevitable.
Which of the features discussed in the list above are nice to have?
Which are required? Not all of these are required to achieve
improvement. What are most important?
Among the participants there was consensus that supporting signatures
(for integrity and authentication) of the firmware image itself and
the need for partial updates was seen as important.
There were, however, also concerns regarding the performance
implications since certain device categories may not utilize public
key cryptography at all and hence only a symmetric key approach seems
viable, unless some other scheme such as hash-based signature become
practical (they currently aren't due to signature size). This aspect
raised concerns and trigger a discussions around the use of device
management infrastructure, similar to Kerberos, that manages keys and
distributes them to the appropriate parties. As such, in this set-up
there could be a unique key shared with the key distribution center
but for use with specific services (such as a software update
service) a fresh and unique secret would be distributed.
In addition to the requirements for the end devices there are also
infrastructure-related requirements. The infrastructure may consist
of servers in the local network and/or various servers deployed on
the Internet. It may also consist of some application layer
gateways. The potential benefits of having such a local server might
include:
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- The local server acting for neighbouring nodes. For example, in a
vehicle one micro-controller can process all firmware updates and
redistribute the relevant parts of those to interconnected micro-
controllers.
- Local infrastructure could perform some digital signature checks
on behalf of the devices, e.g., certificate revocation checking.
- Local multicast can enable transmission of the same update to many
devices
- Local servers can hide complexity associated with NAT and
Firewalls from the device
Another point related to local infrastructure is that since many IoT
devices will not be (directly) connected to the Internet, but only
through a gateway, there may in any case be a need to develop a
software / firmware update mechanism that works in environments where
no end-to-end Internet connectivity exists.
Some current firmware update schemes need to identify devices.
Different design approaches are possible.
- In an extreme form in one case the decision about updating a
device is made by the infrastructure based on the unique device
identification. The operator of the firmware update
infrastructure knows about the hardware and software requirements
for the IoT devices, knows about the policy for updating the
device, etc. The device itself is provisioned with credentials so
that it can verify a firmware update coming from an authorized
device.
- In another extreme the device has knowledge about the software and
hardware configuration and possible dependencies. It consults
software repositories to obtain those software packages that are
most appropriate. Verifying the authenticity of the software
packages/firmware images will still be required.
Hence, in some deployed software update mechanisms there is no desire
for the device to be identified beyond the need to exchange
information about most recent software versions. For other devices,
it is seen as important to identify the device itself in order to
provide the appropriate firmware image/software packages.
Related to device identification various privacy concerns arise, such
as the need to determine what information is provided to whom and the
uses to which this information is put. For IoT devices where there
is a close relationship to an individual (see [RFC6973]) privacy
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concerns are likely higher than for devices where such a relationship
does not exist (e.g., a sensor measuring concrete). The software /
firmware update mechanism should, however, not make the privacy
situation of IoT devices worse. The proposal from the group was to
introduce a minimal requirement of not sending any new identifiers
over an unencrypted channel as part of an update protocol.
Software update will however provide yet another venue in which the
tension between those advocating better privacy and those seeking to
monetize information will play out. It is in the nature of software
update that it requires devices to sometimes "call home" and such
interactions provide fertile ground for monetization.
4. Authorizing a Software / Firmware Update
There were quite a few points revolving around authorization.
- Who can accept or reject an update? Is it the owner of the
device, or the user or both? The user may not necessarily be the
owner.
- With products that fall under a regulatory structure, such as
healthcare, you don't want firmware other than what has been
accredited.
- In some cases it will be very difficult for a firmware update
system to communicate to users that an update is available. Doing
so may requires tracking the device and it's status with regards
to the installed firmware/software, with all the privacy downsides
if such tracking is badly done.
- Not all updates are the same. Security updates are often treated
differently compared to feature updates and the authorization for
these may differ.
- Some people may choose to decline updates, often on the basis that
their system is currently stable, but also possibly due to
concerns about unwanted changes, such as the HP printer firmware
update pushed in March 2016 [HP-Firmware] that turned off features
that end-users liked.
5. End-of-Support
There was quite a bit of discussion about end-of-support for
products/devices and how to handle that.
- How should end-of-support, or end-of-features be treated? Devices
are often deployed for 10+ years (or even longer in some
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verticals). Device-makers may not want or be able to support
software and services for such an extended period of time. Will
these devices stop working after a certain, previously unannounced
period of time, such as Eye-Fi cards [eyefi].
- There will be a broad range of device-makers involved in IoT, who
may differ substantially in terms of how well they can handle the
full device life-cycle. Some will be large commercial enterprises
who are used to dealing with long device life times, whilst others
may be very small commercial entities where the device lifetime
may be longer than the company life-time. Yet other devices may
be the result of open-source activities that prosper or flounder.
The problem of end-of-support arises in all these cases, though
feasible solutions for software update may substantially differ.
In some cases device-makers may not be willing to continue to
update devices, for example due to a change in business strategies
caused by a merger. In yet other cases a company may have gone
bankrupt.
- While there are many legal, ethical, and business related
questions can we technically enable transfer of device service to
another provider? Could there even be business models for
entities that take over device updates for original device-makers
who no longer wish to handle software update?
- The release of code, as it was done with the Little Printer
manufactured and developed by a company called Berg
[LittlePrinter], could provide a useful example. While the
community took over the support in that case, this can hardly be
assumed in all cases. Just releasing the source code for a device
will not necessarily motivate others to work on the code, to fix
bugs or to maintain a service. Nevertheless, escrowing code so
that the community can take it over if a company fails is one
possible option.
- The situation gets more complex when the device has security
mechanisms to ensure that only selected parties are allowed to
update the device (which is really a basic requirement for any
secure software update). In this case, private signing keys (or
similar) may need to be made available as well, which could
introduce security problems for already deployed software. In the
best case it changes assumptions made about the trust model and
about who can submit updates.
- How should deployed devices behave when they are end-of-support
and support ends? Many of them may still function normally, but
others may fail due to the absence of cloud infrastructure
services. Some products are probably expected to fail safely,
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similarly to a smoke alarm that makes a loud noise when the
battery becomes empty. Cell phones without a contract can, in
some countries, still be used for emergency services (although at
the expense of the society due to untraceable hoax calls), as
discussed in RFC 7406 [RFC7406].
The recommendation that can be provided to device-makers and users is
to think about the end-of-support, end-of-support scenarios ahead of
time and plan for those. While device-makers rarely want to consider
what happens if their business fails it is definitely legitimate to
consider scenarios where they are hugely successful and want to
evolve a product line instead of supporting previously sold products
forever. Maybe there is also a value in subscription-based models
where product and device support is only provided as long as the
subscription is paid. Without a subscription the product is
deactivated and cannot pose a threat to the Internet at large.
6. Incentives
Workshop participants also discussed how to create incentives for
companies to ship software updates, which is particularly important
for products that will be deployed in the market for a long time. It
is also further complicated by complex value chains.
- Companies shipping software updates benefit from improved
security. Their devices are less likely to be abused as a vector
to launch other attacks, whether on their own networks, or (as
part of a botnet) on other Internet hosts. This clearly creates
an incentive to support and use software updates.
- On the other hand updates can also break things. The negative
customer experience can be due to service interruptions during or
after the update process but can also result from bad experience
from deliberate changes introduced as part of an update - such as
a feature that is not available anymore, or that a "bug" that
another service has relied upon being fixed.
- For most classes of device, there does not seem to be a regulatory
requirement to report or fix, vulnerabilities, similar to data
breach notification laws.
- Subscription models for device management were suggested so that
companies providing the service have an economic interest in
keeping devices online (and updated for that).
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Internet-Draft IoTSU Report February 20177. Measurements and Analysis
From a security point of view it is important to know what devices
are out there and what version of software they run. One workshop
paper [plonka] reported measurements with initial done on buggy
devices first distributed in 2003 that were still detectable in
significant numbers just before the workshop 13 years later. As
such, in addition to the firmware update mechanism companies have
been offering device management solutions that allow OEMs to keep
track of their devices. Tracking these devices and their status is
still challenging since some devices are only connect irregularly or
are only turned on when needed (such as a hockey alarm that is only
turned on before a match).
Various stakeholders have a justified interest in knowing something
about deployed devices. For example,
- Manufacturers and other players in the supply chain are interested
to know what devices are out there, how many have been sold, what
devices are out there but have not been sold. This could help to
understand which firmware versions to support for how long.
- Device users, owners, and customers these may want to know what
devices are installed over a longer period of time, what software/
firmware version is the device running, what is uptime of each of
these devices, what types of faults have occurred, etc. Forgotten
devices may pose problems, particularly if they (have the
potential to) behave badly.
- To an extent, network operators offering services to device owners
and other actors may also need similar information, for example to
control botnets.
- Researchers doing analysis on the state of the Internet ecosystem
(such as what protocols are being used, how much data IoT devices
generate, etc. need measurements for their work.
There can easily be some invasiveness in approaches to acquiring such
measurements. The challenge was put forward to find ways to create
measurement infrastructures that are privacy preserving. Arnar
Birgisson noted that there are privacy-preserving statistical
techniques, such as RAPPOR [RAPPOR], and Ned Smith added that
techniques like Intel's Enhanced Privacy ID (EPID) may play a role in
maintaining some level anonymity for the IoT device (owners) while
also enabling measurement. It seemed clear that naive approaches to
measurement (e.g., where devices are willing to expose a unique
identifier to anyone on request) are unlikely to prove sufficient.
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Internet-Draft IoTSU Report February 20178. Firmware Distribution in Mesh Networks
There was some discussion of the requirements for mesh-based
networks, mainly relating to industrial lighting. In these networks,
software update can impose unacceptable performance burdens,
especially if there are many devices, some of which may be are
sleepy.
The workshop discussed whether some forms of multicast (perhaps not
IP multicast) would be needed to provide acceptable solutions for
software update in such cases. It was not clear at which layer a
multi-cast solution might be effective in such cases, though there
did seem to be no clearly applicable standards-based approach that
was available at the time of the workshop.
9. Compromised Devices
There was a recognition that there are, and perhaps always will be,
large numbers of devices that can be, or have been compromised.
While updating these can mitigate problems, there will always be new
devices added to networks that cannot be updated (for various
reasons) so the question of what, if anything, to do about
compromised devices was discussed.
- There may be value if it were possible to single out a device,
which shows faulty behavior or has been compromised, and to shut
that down in some sense.
- Prior work in the IETF on Network Endpoint Assessment (NEA) [NEA]
allowed assessing the "posture" of devices. Posture refers to the
hardware or software configuration of a device and may include
knowledge that software installed is up-to-date. The obtained
information can then be used by some network infrastructure to
create a quarantined region network around the device.
- RFC 6561 [RFC6561] describes one scheme for an ISP to send
"signals" to customers about hosts (usually those that are part of
a botnets or generating spam) in their home network.
- Neither RFC 6561 nor NEA has found widespread deployment. Whether
such mechanisms can be more successful in the IoT environment has
yet to be studied.
The conclusion of the discussion at the workshop itself was that
there is some interest to identify and stop misbehaving devices but
the actual solution mechanisms are unclear.
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Internet-Draft IoTSU Report February 201710. Miscellaneous Points
There were a number of points discussed at the workshop that don't
neatly fit under the above headings but that are worth recording.
Those included:
- Complex questions can arise when considering the impact of the
lack of updates on other devices, other persons, or the public in
general. If I don't update my device and that is used to attack a
random host on the Internet, then what incentive do I have to do
updates? What incentive has my device's vendor to have done that
in advance? An example of such a case can be found in DDoS
attacks from IoT devices, such as printers [SNMP-DDOS] and cameras
[DDOS-KREBS].
- With some IoT devices there are many stakeholders contributing to
the end product (e.g., contributing different subsystems) and
ensuring that vulnerabilities are fixed and software/firmware
updates are communicated through the value chain is known to be
difficult, as demonstrated in [OS14].
- What about forgotten devices? There are many such, and will be
more. Even though they are forgotten, such devices may be useless
consumers of electricity, or may be part of some critical system.
- Can we determine whether an update impacts other devices in the
Internet? Updates to one device can have unintended impact on
other devices that depend on it. This can have cascading effects
if we are not careful. Changing the format of the output of a
sensor could have cascading impacts, e.g., if some actuator reacts
to the presence/absence of that sensor's data.
- How should a device behave when it is running out-of-date
software. The example of a smoke alarm was mentioned. We don't
want 100 devices in a living room to start beeping when their
batteries run low or when they cannot communicate with the cloud.
But are devices supposed to simply stop working?
- The IETF has published a specification that uses the Cryptographic
Message Syntax (CMS) to protect firmware packages, as described in
RFC 4108 [RFC4108], which also contains meta-data to describe the
firmware image itself. During the workshop the question was
raised whether a solution will in future be needed that is post-
quantum secure. A post-quantum cryptosystem is a system that is
secure against quantum computers that have more than a trivial
number of quantum bits. It is open to conjecture whether it is
feasible to build such a machine but current signature algorithms
are known to not be post-quantum secure. This would require
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introducing technologies like the Hash-based Merkle Tree Signature
(MTS) [housley-cms-mts-hash-sig], which was presented and
discussed at the workshop. The downside of such solutions are,
their novelty, and for these use-cases, the fairly large signature
or key sizes involved, e.g., depending on the parameters a
signature could easily have a size of 5-10KiB [hashsig]. While it
is likely that post-quantum secure signature algorithms will be
needed for software update at some point in time, it may be the
case that such algorithms will be needed sooner for services
requiring long term confidentiality, (e.g., using TLS) so it was
not clear that this application would be a first-mover in terms of
post-quantum security.
- Many devices that use certificates do not check the revocation
status of certificates, even though extensions like OSCP stapling
exists [RFC6961] and is increasingly deployed with Web browsers.
The workshop participants were inconclusive regarding the
recommendations of certificate revocation checking although the
importance has been recognized. The reluctance of deploying
certificate revocation deserves further investigations.
11. Tentative Conclusions and Next Steps
The workshop participants discussed some tentative conclusions and
possible next steps:
- There was good agreement that having some standardized secure
(authorized and authenticated) software update would be an
improvement over having none.
- It would be valuable to find agreement on the right scope for a
standardized software/firmware update mechanism. It is not clear
that an entire update system can or should be standardised but
there may be some aspects of such solutions where standards would
be beneficial, e.g., (meta-)data formats and/or protocols for
distributing firmware updates. More discussion is needed to
identify which parts of the problem space could benefit from
standardisation.
- It will be useful to investigate solutions to install updates with
no operation interruption as well as ways to distribute software
updates without disrupting network operations (specifically in
low-power wireless networks), including the development of a
multicast transfer mechanism (with appropriate security).
- There will almost certainly be a need for a way to transfer
authority/responsibility for updates, particularly considering
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end-of-support cases. This is very close to calling for a
standard way to "root" devices as a feature of all devices.
- We would benefit from documentation of proofs-of-concept of
software/firmware updates for constrained devices on different
operating system architectures. The IETF Light-Weight
Implementation Guidance (lwig) working group may be a good venue
for such documents.
12. Security Considerations
This document summarizes an IAB workshop on software/firmware updates
and the entire content is therefore security related. Standardizing
and deploying a software/firmware update mechanism for use with IoT
devices could help to fix security vulnerabilities faster and in some
cases the only via to get vulnerability patched at all.
13. IANA Considerations
This document does not contain any requests to IANA.
14. Acknowledgements
We would like to thank all paper authors and participants for their
contributions. The IoTSU workshop is co-sponsored by the Internet
Architecture Board and the Science Foundation Ireland funded CONNECT
Centre for future networks and communications. The programme
committee would like to express their thanks to Comcast for
sponsoring the social event.
15. Appendix A: Program Committee
The following individuals helped to organize the workshop: Jari
Arkko, Arnar Birgisson, Carsten Bormann, Stephen Farrell, Russ
Housley, Ned Smith, Robert Sparks, and Hannes Tschofenig.
16. Appendix B: Accepted Position Papers
The list of accepted position papers is below. Links to these, and
to the workshop agenda and raw minutes are accessible at:
<https://down.dsg.cs.tcd.ie/iotsu/>.
- R. Housley, 'Position Paper for Internet of Things Software
Update Workshop (IoTSU)'
- D. Thomas and A. Beresford, 'Incentivising software updates'
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